According to reports from various sources on the morning of 21-July-2000, the Volcano Lascar had a small eruption of approximately 2 hours of duration (10:30-12:30 local time). The smoke column reached a maximum height of 4,000 m on the crater, which is of low intensity in comparison with similar eruptions registered 15 years ago. The slopes of the crater remain very unstable due to the last great eruption in April of 1993. The recent eruption was clearly visible from Chuquicamata, 150 km toward north, to astronomers at the CBI site on Chajnantor, and to attendees at a gravitational lensing conference in San Pedro de Atacama. According to information of Customs officers of San Pedro de Atacama and Toconao (35 km to the west), the dispersed ash moved toward the northeast, and would not have fallen in Chilean territory. The eruption was accompanied of a small tremor till 10:35 hrs and underground noises. The ALMA seismometer was being refitted with a hardware upgrade and was not present at the site.
The vulcanologists concluded that this event corresponded to a small eruption characteristic of periods of degassing of the volcano, that take place when high parts of the volcanic conduit become clogged. This clogging was preceded by a loss of the height of the smoke column from Lascar during last the two months. It is not clear if this is a small and discrete event or the precursor of greater activity. There was no ash fall on or near the ALMA site, and CBI observations continued throughout the activity.